Extensible boom with buckling-prevention

ABSTRACT

In an extensible boom of the type having telescopically extensible boom members, a buckling-preventing method for hydraulic cylinder unit employed in the boom wherein an intermediate position of an optionally extended piston-rod of said cylinder unit is always supported with a buckling-preventing device having legs slidably or rotatably engaged with inner circumference of a boom member. The present invention further includes driving means for said buckling-preventing device which moves the device to said intermediate position of the piston-rod in connection with the operation of said cylinder unit.

United States Patent [1 1 Sakamoto et a1.

1 1 Mar. 27, 1973 15 1 EXTENSIBLE BooM WITH BUCKLING-PREVENTION [76]Inventors: Teruya Sakamoto, 2482-10 Midoricho, Sakaide; TakemiNishimura, 230-14 Nonowe, Havikino; .Osamu Takarada, 1475 Omachi,Mure-cho,

Kita-Gun, all of Japan 221 Fileda Oct. 15,1970 21 App1.No.: 80,913

[] Foreign Application Priority Data 12111.31, 1970 Japan /8718 Feb. 2,1970 Japan ..'....45/9452 [52 U.S.Cl. ..52/121,.52/115,212 /55 51] Int.Cl. ..E04h 12/34 [58] Field of Search ..52/l11, 112, 121, 115; 212/55;92/117,l26,137,165

[56] References Cited UNITED STATES PATENTS 1,751,348 3/1930v Mitchell..52/121 1,244,784 10/1917 Schi1der'.... ...92/137 2,645,213 Huber.;92/126 3,431,825 3/1969 Crawley et al. ..92/ l R 3,464,169 9/1969Potain ..52/1 15 FOREIGN PATENTS OR APPLICATIONS 1,217,041. 3/1966Germany ,.2l2/55 1,268,804 3/1968 Germany,

996,853 6/1965 Great Britain Primary Examiner Frank L. Abbott AssistantExaminer-Leslie A. Braun Artomey-Olson, Trexler, Wolters & Bushnell 7]ABSTRACT In an extensible boom of the type having telescopicallyextensible boom members, a buckling-preventing method for hydrauliccylinder unit employed in the boom wherein an intermediate position ofan optionally extended piston-rod of said cylinder unit is alwayssupported with a' buckling-preventing device havinglegs slidably orrotatably engaged with inner circumference of a boom member. The presentinvention further includes driving means for said bucklingpreventingdevice which moves-the .device to said intermediate position of thepiston-rod in connection with the operation of said cylinder unit.

Figures PATENTEUHARZYIHH 3 722,154

SHEET 4 BF 7 INVENTORS 751 1 90 Jain/r2022 BY Qaam 220 m PATENTEUMAMIMSHEET 5 OF 7 I N VE NTORS ATTORNEYS.

EXTENSIBLE BOOM WITH BUCKLING- PREVENTION SUMMARY OF THE INVENTION Thisinvention relates to an extensible boom of the type havingtelescopically extensible boom members, and more particularly to abuckling-preventing method for hydraulic cylinder unit employed in theboom of the aforementioned type and an apparatus therefor.

DISTINCT IONS OVER THE PRIOR ART AND OBJECTS In an extensible boom for acrane comprising an inner boom member telescopically inserted into anouter boom member, there is arranged a hydraulic cylinder unit forextending and contracting the boom. That is, in the extensible boom, thepiston-rod of said cylinder unit is connected at the free end thereof tothe outer or inner boom member, and the cylinder of said unit isconnected at a suitable portion thereof to the other boom member, sothat the extensible boom is extended or contracted as the hydrauliccylinder unit is extended or contracted. A compressive stress applied tothe extensible boom is supported by the hydraulic cylinder unit, so thatextremely high compressive stress is applied to the unit during loadingand unloading works with a crane.

When the extensible boom or the hydraulic cylinder unit is extended, theresistivity against buckling of the cylinder unit, especially thepiston-rod of said unit, namely the resistivity against the braking dueto buckling stress applied to the extended piston-rod, is decreased withthe increase in extension of the boom, and more exactly of the span ofextended piston-rod determined with the length of each boom member. Inother words, the longer the span is, the higher resistivity againstbuckling is required.

On the other hand, a crane with a high lift is required recently, sothat each boom member of an extensible boom for a crane becomes verylong whereby a longer piston-rod of a hydraulic cylinder unit becomesrequired for extending and contracting such a long boom member.

When the span of an extended piston-rod becomes longer,-a piston-rodwith a larger diameter is usually used for giving a required strengthagainst buckling to the same. However, when the diameter of thepistonrod is increased, then the hydraulic cylinder unit becomeslarge-scaled and is increased in weight and in cost. There have neverbeen proposed methods or apparatus for avoiding these defects.

Accordingly, the primary object of the present invention is to provide anovel buckling-preventing method for hydraulic cylinder unit employed inan extensible boom by which above defects are fully avoided and whichguarantees the exclusion of the bending of extended piston-rod due tobuckling stress applied to the rod.

Another object of the present invention is to provide abuckling-preventing method for hydraulic cylinder unit which utilizesboom members skillfully so as to achieve the primary object in a simplemanner.

The above objects are attained according to the present invention byproviding a buckling-preventing device which comprises a portionslidably received with the piston-rod and legs slidably or rotatablyengaged with the inner circumference of the boom, and by moving saiddevice into a predetermined intermediate position between the free endof the piston-rod and the end of the cylinder in connection with theextending and contracting operation of hydraulic cylinder unit.

The present invention further aims at the provision of driving methodand means for the aforementioned buckling-preventing device which allowto move the device into said predetermined position in a desirablemanner.

BRIEF DESCRIPTION OF TI IE DRAWINGS The present invention and itsadvantages will become more readily apparent as the specification isconsidered in conjunction with the accompanying drawings in which:

FIG. I is a sectional side view of an embodiment of two-stage extensibleboom according to the present invention showing a contracted state andtaken along line 1-1 of FIG. 3;

FIG. 2 is a sectional side view of the extensible boom shown in FIG. 1showing an extended state;

FIG. 3 is a sectional view taken along line 33 of FIG. 2;

FIG. 4 is a sectional side view of another embodiment of a two-stageextensible boom according to the present invention;

FIG. 5 is a sectional side view of still another embodiment of athree-stage extensible boom according to the present invention;

FIG. 6 is a sectional side view of a further embodiment of a two-stageextensible boom according to the present invention;

FIG. 7 is a sectional side view of a still further embodiment of atwo-stage extensible boom according to the present invention;

FIG. 8 is a sectional side view of another embodiment of a three-stageextensible boom according to the present invention;

FIG. 9 is a sectional side view of still another embodiment of atwo-stage extensible boom according to the present invention;

FIG. 10 is a sectional view taken along line 1010 of FIG. 9;

FIG. 11 is a sectional side view of a further embodiment of a two-stageextensible boom according to the present invention;

FIG. 12 is a side view of another embodiment of employed rollersaccording to the present invention;

FIG. 13 is a still further embodiment of a three-stage extensible boomaccording to the present invention;

FIG. 14 is a side view showing the relation between plate members androllers;

FIG. 15 is a sectional side view of another embodiment of a two-stageextensible boom according to the present invention;

FIG. 16 is an enlarged perspective view of the drum shown in FIG. 15;

FIG. 17 is a sectional side view of still another embodiment of atwo-stage extensible boom according to the present invention;

FIG. 18 is a sectional view of the extensible boom taken along linel8-l8 of FIG. 17;

FIG. 19 is a sectional side view of a further embodiment of a two-stageextensible boom according to the present invention;

FIG. 20 is a sectional side view of a still further embodiment of atwo-stage extensible boom according to the present invention;

FIG. 21 is a sectional side view of another embodiment of a two-stageextensible boom according to the present invention;

FIG. 22 is an enlarged sectional view taken along line 22-22 of FIG. 21;

FIG. 23 is a sectional view taken along line 2323 of FIG. 22;

FIG. 24 is a sectional side view of a still further embodiment of atwo-stage extensible boom according to the present invention showing anextended state;

FIG. 25 is a sectional side view of the extensible boom shown in FIG.24;

FIG. 26 is an enlarged sectional side view, partly cutaway, of a part ofthe extensible boom shown in FIG. 25;

FIG. 27 is a sectional view taken along line 2727 of FIG. 26; and

FIG. 28 is a rear view of the part shown in FIG. 26.

DETAILED DESCRIPTION Referring now to the drawings, wherein likenumerals designate like parts throughout the various figures thereof,one embodiment of an extensible boom, constructed in accordance with thepresent invention is designated by the reference numeral 1 andillustrated in FIGS. 1, 2 and 3.

The extensible boom 1 includes an outer boom member 2 telescopicallyreceiving an inner boom member 3 therein and an inverted hydrauliccylinder unit 4, the piston-rod 5 of which is pivotally connected at itsfree end portion to the lower end portion of the outer boom member 2 bysuitable means such as pin 6 and the cylinder 7 of which is pivotallyconnected at one end portion to the lower end portion of the inner boommember 3, as generally indicated by the reference numeral 8.

In accordance with the present invention, a bucklepreventing device 9 isprovided within the boom 1 and comprises supporting legs 10 with shoes10a slidably engaged with the inner circumference of the outer boommember 2 and a boss 11 slidably mounted on the piston rod 5. The shoes10a may be interchanged with rollers 10b shown in FIG. 9.

The device 9 further includes two pulleys l2 and 13 the shafts of whichare secured to legs 10. One of the pulleys 12 trains or carries a wirerope 14 which is suitably fastened at one end to the lower end of theinner boom member 3 at 15, the rope extending around the pulley 12 inU-letter-shaped manner and being suitably fastened at the other end tothe upper end of the outer boom member 2 at 16. In like fashion, pulley13 trains or carries a wire rope 17 which is fixed at one end to thelower end of the inner boom member 3 at 18, and which is turned in aU-letter-shaped manner successively at a pulley 19 rotatably mountedonto the upper end of the outer boom member 2, a pulley 20 rotatablymounted onto the lower end of the boom member 2 and the pulley 13, therope being fixed at the other end to the lower end of the outer boommember 2 at 21.

With the buckle-preventing device connected to extensible boom 1 in theaforementioned manner, wire rope 14 causes boss 11 and supporting legs10 to move forwardly or away from the pin 6 as cylinder 7 moves the boomto its extended position. More particularly, the incremental movement ofboss 11 is one-half that of piston 7, so that the boss always ismaintained equivalent distances from the cylinder and the free end ofthe piston-rod 5. As illustrated in FIG. 2, when cylinder 7 has moved adistance L, boss ll has moved a distance one-half L. In like manner,boss 11 is moved downwardly or towards pin 6 by the wire rope 17 whenthe extensible boom 1 is contracted, the boss continuously beingmaintained equivalent distances from the cylinder and pin 6.

It is to be understood that, for sake of clarity, the pulleys l2 and 13have been illustrated as being mounted on individual shafts which extendaxially along different lines and do not lie on a same line asillustrated in the embodiment shown in FIGS. 1, 2 and 3. for a smoothoperation it is preferable to mount both of the pulleys on a commonshaft or on respective shafts lying on a common line.

In addition, although an inverted hydraulic cylinder unit 4 andtwo-stage boom have been shown, it is to be understood that the presentinvention can be applied to a boom with a normally postured hydrauliccylinder unit (see FIG. 4) and also to a multistage extensible boomhaving more than three boom members (see FIG. 5). In FIG. 5, numeral 4designates an additional hydraulic cylinder unit for a third boommember, numeral 9 designates an additional buckle-preventing device, and14, and 17 designate wire ropes for moving the additional device 9 inthe three stage extensible boom in connection with the extending andcontracting operations of the cylinder unit 4 respectively.

Each of the embodiments of the present invention shown in FIGS. 1through 5 provides driving means for buckle-preventing device whereinsaid device is moved by a wire rope which is fixed at one end to asuitable portion of a boom member carrying a cylinder of a hydrauliccylinder unit, is trained over a pulley provided in thebuckle-preventing device in such a manner that said rope is turned atsaid pulley in U-letter-shaped manner, and is fixed at the other end toan end of a boom member carrying a piston-rod of said cylinder unit,atwhich end the latter boom member is integrated with the former boommember, and a wire rope, which is fixed at one end to said integratedend of the former boom member, is trained over two pulleys rotatablymounted onto both ends of the latter boom member and another pulleyprovided in the buckle-preventing device successively in such a mannerthat said latter rope is turned at each of said latter three pulleys inU- letter-shaped manner, and is fixed at the other end to thenon-integrated end of the latter boom member.

Turning to FIG. 6, a further embodiment of the present invention isillustrated. In this embodiment, four equally circumferentially spacedelongated racks 22 (only two of which are shown) are secured to theexternal sides of cylinder 7 and extend parallel to the extending andcontracting direction of an extensible boom 1. As illustrated in FIG. 6,the racks 22 extend from the right end of the cylinder and terminateapproximately in the middle thereof. In addition, four elongated racks23 are provided on the inner surface of the inner boom member 3 inConfronting face-to-face relationship to respective racks 22, the racks23 extending from the left end of member 3 to approximately themiddlethereof. Four pinions 24 (two of which are shown) are provided onopposite sides of cylinder 4 and engage confronting racks 22 and 23, .asillustrated buckle-preventing device 9 by means of rods25.

It isreadily apparent that as the piston 5 of FIG. 6 is moved betweenits contracted and extended position for moving inner boom member 3 in asimilar manner, the racks 23 are-moved the same distance relative tostationary racks 22. In this manner, the pinions 24, through connectingrods 25, move device 9 one-half of this distance, in the extending orcontracting direction of the boom 1, whereby the device is alwayspositioned at an intermediate position between the free end of theextended piston-rod 5 and the cylinder 7.

In addition, when the pinions 24 are engaged with racks 22 provided onthe outer circumference of the cylinder 7 at equally circumferentiallyspaced intervals (only racks 22 at upper and lower sides are shown inFIG. 6), the free end of the cylinder 7 is supported to the inner boommember 3 by the four pinions 24 so that the hydraulic cylinder unit 4 isgiven an increased resistivity against buckling thereof.

Although a normally postured hydraulic cylinder unit 4 is employed inthe embodiment shown in FIG. 6, driving means for the buckle-preventingdevice 9 comprising racks and pinions can also be employed when aninverted or upside-down hydrauliccylinder unitis used, as, for example,shown in FIG.-7. In the embodiment shown in FIG. 7, a fixed rack 23 issecured on the inner longitudinal circumference of the inner boom member3 and in confronting relationship with a rack 22 which is fixed at oneend to the lower end of an outer boom member 2 at 26 and whichextendsinto inner boom member 3 where it is attached to a roller 27 androtatable within and .along the lower end of the inner boom. while theroller 27 is shown attached to rack 22 and movable along the innersurface of boom member 3, it is to be understood that the rollermay befixed to the inner boom and positioned in rotatable engagement with theback of the rack 22 for serving the same function. In either case, theracks include a pinion 24 and rod connected to device 9 for movingdevice 9 in the same manner as discussed with regard to FIG. 6.

It is to be understood that driving means for the buckle-preventingdevice 9 comprising a combination of racks and pinions .can also beemployed to a multistage extensible boom having more than three boommembers, as shown, for example, in FIG. 8. In FIG. 8, numeral 4,designates an additional hydraulic cylinder unit for a third boommember, numeral 9 designates an additional buckle-preventing device,22', and 23 and 25 an additional connecting rod, respectively, all ofwhich operate in the-same manner as described with respect to FIGS. 6and 7.

Each of embodiments of the present invention shown in FIGS. 6, 7 and 8provides another driving means for the buckle-preventing device whereinsaid device is moved by bearing means for a pinion or pinions engagingwith a pair of racks at the same time which racks are provided atdefinite portions on the cylinder of a hydraulic cylinder unit or a boommember carrying said cylinder and on a boom member carrying thepiston-rod of said cylinder unit in face-to-face and parallel relation.

Turning to FIGS. 9 and 10, attention is directed to another embodimentof the present invention. In the extensible boom 1 shown in FIGS. 9 and10, four equally circumferentially spaced rollers 28 covered withplastic tires such as gum tires are provided between and in engagementwith the upper half portion of a cylinder 7 and the lower half portionof an inner boom member 3. The bearings29 of rollers 28 areconnected toa buckle-preventing device 9 by rods 30. This construction provides anadvantage over the embodiments of FIGS. 7 and 8 in that there is no needfor the aforementioned racks. In this extensible boom 1, when thepiston-rod 5 is extended by an optional distance, the rollers are movedor rolled along the outer circumference of the cylinder 7 and the innercircumference of the boom member 3 so that the device 9 is moved withthe rollers 28 by a distance one-half of extended distance of thepiston-rod 5, whereby the device 9 is always positioned at anintermediate position between the free end portion of the extendedpiston-rod 5 and the lower end of the cylinder 7.

With the utilization of at least a pair of rollers 28 provided on theouter circumference of the cylinder 7, as is the case in the embodimentshown in FIGS. 9 and 10,

i and in the event of a buckling load being applied to the cylinder unit4, at least one of the rollers 28 will always bein engagement with boththe cylinder 7 and the inner boom member 3', whereby the movement of thedevice 9 toward the extending or contracting direction is guaranteedmore surely than if only a single roller 28 were provided. However, whenfour rollers 28 are arranged equally circumferentially around thecylinder 7, as illustrated in FIG. 10, the free end portion of cylinder7 is supported to the inner boom member 3' through these four rollers28, for enhancing the resistivity against buckling of hydraulic cylinderunit 4 at the portion thereof where the rollers 28 are positioned.

FIG. 11 shows a modification of the embodiment shown in FIGS. 9 and 10.In this embodiment wherein aninverted or upside-down hydraulic cylinderunit 4 is arranged in an extensible boom 1, there is provided anadditional plate member 31, one end of which is fixed at 32 to the lowerend portion of an outer boom member 2 which is also connected to apiston-rod 5 of the cylinder unit 4, the plate member extendinglongitudinally into inner boom member 3, as illustrated in FIG. 1 1.Further, a pair of rollers 28 are positioned for rolling engagementbetween and to plate member 31 and an inner boom member 3, the bearingsof rollers 28 being connected to a buckle-preventing device 9 by rods30, so that device 9 can be movedwith aid of the rolling action of therollers 28 in the same manner as described in the embodiment shown inFIGS. 9 and 10.

FIG. 12 shows a modification of the rollers 28 used in the aboveembodiment of FIG. 11, which modification is directed towards reducingthe diameters of such rollers as well as the need for rollers withaccurately dimensioned diameters. In this preferred modification,

a plurality of rollers 28,, 28 and 28 are provided and I are rotatablymounted on bearing means 34 pivotally connected to the end of rod 30 at33, the rollers operating in connection with one another. The rollers28;, and 28 which pivot about intermediate roller 28 along with bearingmeans 34, are respectively forced against the inner boom member'3 andthe plate member 31 with aid of a spring 35 provided in the bearingmeans 34, respectively. In this manner, the rollers 28,, 28 and 28provide the same function as a single roller 28 of FIG. 11. v

It is to be understood that thedriving means for the buckle-preventingdevice 9' used in the embodiment shown in FIG. 11 can also be applied toa multi-stage extensible boom having three or more boom members .byproviding the required numbers of plate members 31. In the three-stageextensible boom shown-in FIGS. 13 and 14, plate members 31a and 31b arefixed at common ends thereof to respective boom members 1 and 2 at 32aand 32b and are supported at their free end portions, by the means shownin FIG. 14.,That is,

the plate member 31a is engaged between supporting rollers 36a and 36brotatably mounted on one-stage higher boom member 2 so as to keep theplate at a definite position. In addition, bearing means 34a providedwith a roller 28a for moving buckle-preventing device 9a includes tworollers 37 and 37 -positioned on opposite sides of roller 28a.Rollers-37 and 28a receive therebetween and engage opposite sides of theplate member 31a while the rollers 37 and 28a receive therebetween andengage opposite sides of plate member 31b, whereby the plate members 31aand 31b 8' rotating the drum 40 in such a direction that the ropes 45and 46 will be wound up around the drum. When a piston-rod 5 is extendedor contracted by an optional distance, the drum 40 is rotated with oragainst the force of the spring 47 so that the pair of wire'ropes 45 and46 are wound up 'or unwound under tension, whereby the device 9 is movedby a half of the extended or contracted distance of the piston-rodS. In

this way, the device is always positioned at an interj mediate positionbetweenthe free end portion of the. extended piston-rod 5 and the lowerend of the cylinder Though an inverted or upside-down hydraulic cylinderunit 4 and a two stage extensible boom are,

vided with normally postured hydraulic cylinder units,

as can now clearly be understood by those skilled in the art. Thus, thisembodiment further provides compact I driving means for the.buckle-preventing device wherein said device is moved by a rotary drumwhich is rotatably mounted to the device and which is always forced insuch a direction that wire ropes or chains will be wound up on saiddrum, the wire ropes or chains being fixed to the drum at common endsand to the ment of the roller 28a therewith. Furthermore, a roller 28b(FIG. 13) for moving a buckle-preventing device 9b is rotatably engagedagainst the plate member 31c and the inner circumference of the boommember 3, the plate member 31c being fixed at one end to the lower endof boom member 2 and extendinginto boom member 3 as illustrated in FIG.13.

' Any of the embodiments shown in FIGS. 9 through 14 provides drivingmeans for the buckle-preventing device wherein said device is moved by aroller"(rollers) which is (are) slidably engaged with the cylinder, aboom member carrying the cylinder or a plate member fixed to a suitableportion of said boom member, and also a boom member carrying thepistonrod or a plate member fixed to a suitable portion of saidboom'member.

Attention is directed to FIGS. 15 and 16 for a further embodiment of thepresent invention. In this embodiment, a buckle-preventing device 9 isprovided with a rotary drum 40 the longitudinal shaft 39 of which issupported to the device 9 in a direction transverse of the movement ofthe device. Between the drum 40 and the extending and contracting boommembers, there is provided a pair of wire ropes and 46 common ends ofwhich are fixed to an outer boom member 2 and the inner boom member 3,respectively, at suitable positions 41 and 42 (in this case, at thelower end portions of said members) under a condition where the boom 1is fully extended. The otherwise free common ends of ropes'45 and 46 arefixed to the drum 40 at 43 and 44,

respectively. Further, between the drum 40 and the buckle-preventingdevice 9, there is provided a plate spring 47 the ends of which arefixed to the drum 40 at relatively extending and contracting boommembers.

In briefly summarizing the preferred embodiment of the present inventionas illustrated in FIGS. 1 through 16, a device is provided forsubstantially eliminating buckling of a hydraulic cylinder unit which isused for driving an extensible boom. The buckle-preventing device ispositioned around the piston-rod of the cylinder unit within one of theboom members and includes outwardly extending legs which slidably orrotatably engage the inner surface of the boom member for longitudinallymoving the device, therethrough. Various types of driving means (asillustrated in the various figures) are provided for moving the devicealong with the piston-rod (or cylinder component) such that the deviceisalways positioned at substantially an intermediate point between thefree end of the piston-rod and the end of cylinder of said cylinderunit. In this manner, the piston-rod is always supported with thebuckle-preventing device at what is otherwise the critical bucklingpoint whereby resistance against such buckling becomes effectivelyincreased at any extended state of said rod. Therefore, according to thepresent invention, the weight of the hydraulic cylinder unit can bedecreased correspondingly, so that an extensible boom with a longerscale can be obtained without increasing substantial weight and cost.

The following are further detailed embodiments of driving means for thebuckle-preventing device. One

such embodiment is illustrated in FIGS; 17 and 18. In

this embodiment, the buckle-preventing device 9 is spring-biased in thedirection of arrow A by a spring 50a provided between said vdevice 9 anda suitable portion of the cylinder 7. A rod member 52 having a stopper51 at the uppermost portion is slidably inserted through the device andhas its other end secured to the free end portion of piston-rod 5. Inthis manner, the devicev 9 is biased into engagement with the lower endof the cylinder 7, due to the force of the spring 5011, so

long as the hydraulic cylinder unit 4 is in acontracted state or in anextended state with an extended distance equal to or shorter than adefinite L, the effective length of the rod 52. Therefore, the device 9is moved in the outer boom member 2 along with the cylinder 7 throughthe distance L. However, when the piston-rod 5 is extended by a distancegreater than the aforementioned distance L, the rod member 52 preventsfurther movement of the device 9 in the outer boom member (FIG. 17) sothat the span between the device 9 and the pivot 6 of the piston-rod 5is maintained at the aforementioned definite distance L. The distance Lis preferably designed so as to correspondt'o one-half of the fullyextended span of the piston-rod 5, so that the device 9 is positionedsubstantially intermediate the free end of the piston-rod and cylinder7. Further, in theembodiment shown in FIGS. 17 and 18, there is provideda rod member 53 which has one end secured to the device 9, and the otherend, including a stopper 54, slidably inserted into a bracket 55 fixedlymounted on the outer circumference of the cylinder 7. The rod member 53serves for-preventing the interval betweenthe device 9 and the cylinder7 from being enlarged more than the definite one L.

Though an inverted or upside-down hydraulic cylinder unit 4 is employedin the embodiment shown in FIGS. 17 and 18, driving means for the.bucklepreventing device according to the present embodiment can also beapplied to an extensible boom with a normally postured hydrauliccylinder unit 4, as can be understood with reference to FIG. 19.Further, although the device 9 and the cylinder 7 are connected throughspring 50a and a rod member 52 is arranged between the device 9 and thefree end of the piston-rod 5 so as to keep the interval between thedevice 9 and said free end substantially equal to a definite distancewhen the unit 4 is in an extended state (as illustrated in FIG. 19) thedevice 9' may be so constructed that the interval between the device andthe cylinder 7 is maintained fixed (for example, a distance L) when unit4 is in its most extended state. This is achieved by connecting thedevice 9 to the free end of the piston-rod 5 by means of a spring and byarranging the aforementioned type of a rod member between the device andthe cylinder. Furthermore, even if the spring 50a shown in FIG. 17 isomitted, the device 9 will be positioned substantially intermediate thefree end of piston-rod 5 and cylinder 7 when the cylinder unit is in itsfully extended position 'as limited by rod members 52 and 53.

In addition, more than two buckle-preventing devices may be providedwith a piston-rod, as illustrated in FIG. 20. in this embodiment, twobucklepreventing devices 94 and 9b, each of which is constructed in thesame manner as buckle-preventing device 9, are provided about thepiston-rod 5 of cylinder unit 4. These two devices 9a and 9b areconnected to each other with a spring 50b. Further, a rod member 530having an end stopper 54a connects the device 9a and the cylinder'7while a rod member 52b having an end stopper 54b connects the device 9band the free end of piston-rod 5 so that the respective intervalsbetween the device 9a and the cylinder 7 and between the device 9b andthe free end of the pistonrod 5 are maintained fixed when the hydrauliccylinder unit 4 is fully extended.

It is to be understood that the rod members 52, 53, 52b and 53a shown inFIGS. 17 through 20 may be substituted with wire ropes, chains or thelike having definite length. Further, although springs 50a and 50b areof the pulling type as illustrated in FIGS. 17 through 20, compressionsprings may be used for the same purpose when they are arranged inparallel arrangements with the rod members so as to keep said springsstraight.

Each of embodiments of the present invention shown in FIGS. .17 through20 provides another driving meansfor the buckle-preventing devicewherein said device is moved during the extension of a hydrauliccylinder unit by a spring or a rod member while keeping the intervalbetween the device and the free end of the piston-rod or between thedevice and the cylinder fixed when the hydraulic cylinder is in anextended state.

A further embodiment of the present invention is illustrated in FIGS.21, 22 and 23. In this embodiment, restraining means are providedbetween the bucklepreventing" device 9 and an innerboom member (althoughsaid means may be provided between the device 9 and the cylinder 7)which includes a pair of substantially diametrically aligned hooks 59pivotally mounted on brackets 56 at .57 and spring forced in thedirection of arrow B by means of associated springs 58. Each hook 59includes an arm portion having a roller 60 rotatably mounted thereto.Each hook 59 is biased in a position shown in FIG. 21 (the same positionis illustrated by imaginary lines in FIG. 23) when its associated roller60 is in rotatable engagement with the inner circumference of the outerboom member 2.

However, each of the hooks 59 is forced into a restraining position, asillustrated by solid lines in FIG. 23, when its roller 60 engages'anassociated cam surface 61 provided on the inner circumference of theouter boom member 2.

causing the hook 59 to move from its biased position to its restrainedposition for disengaging the hook from pin 62 and therefore disengagingthe hook from device .9. In this manner, the device 9 is restrained at adefinite position in the outer boom member 2, namely at a position apartfrom the free end of the piston-rod 5 by a definite distance Lcorresponding to substantially onehalf of the fully extended span of thepiston-rod 5. The device 9 is kept at this position with the aid ofoptional means such as frictional resistance provided between the device9 and the inner circumference of the outer boom member 2 or between thedevice 9 and the piston-rod 5. When the cylinder 7 extends beyond thispoint, the hooks 59, of course, move back to their biased positions.

When the hydraulic cylinder unit 4 is contracted from its fully extendedstate, the rollers60 again are brought into riding engagement with camsurfaces 60 whereby hooks 59 are driven to their restrained positionsfor receiving associated pins. 62. Further movement of the unit 4towards its contracted position causes the hooks to move to their biasedpositions and into engagement with the pins so that the device 9 isnecessarily moved together with the cylinder 7 when the cylinder unit 4is contracted still further. In addition, there is provided a littlebacklash between the device 9 and the cylinder 7 in said restrainingstate.

In the embodiment shown in FIGS. 21, 22 and 23, an

inverted or upside-down hydraulic cylinder unit 4 is arranged in anextensible boom 1. However, it is to be understood that driving meansforthe buckle-preventing device 9 according to this embodiment can alsobe'applied to an extensible boom in which a normally postured hydrauliccylinder unit is arranged, as hereinafter detailed with reference to theembodiment shown in FIGS. 24 through28. In this embodiment, there areprovided particular restraining means which limit the buckle-preventingdevice 9 to a desired intermediate position on the extended piston-rodwithout relying upon the aforementioned frictional resistance, or thelike.

Specifically, bracket 63 (FIG. 26) is secured to the top portion of thecylinder 7 upon which a first hook 64 is pivotally mounted at 65, thehook being spring biased in the direction of arrow C by spring means 69.A roller 66 is pivotally mounted on one end portion of first hook 64.While the first hook 64 is always restrained by a stopper 67 projectingfrom bracket 63, or a pin 68 projecting from device 9, the hook is movedinto the reverse direction of arrow C and out of engagement with the pin68 when the roller 66 rides on a cam 70 member 3 at an intermediateposition thereof.

Turning to FIG. 28, a second book 72 is pivotally mounted to the innercircumference of the inner boom member 3, at a point 73 in approximatelythe middle of the boom member, the second hook 72 being spring forced orbiased in the direction of arrow D by means of a spring 71. In itsbiased position, the second hook 72 is restrained by a pin 74 projectingfrom theinner boom member 3. The base end of a lever 75 is pivotallyconnected to the inner circumference of boom member 3 at 76, and aspring 77 is arranged between the other end of lever 75 and a suitableportion of the second hook 72. The second hook 72 is restrained with theforce of spring 71 on the aforementioned pin 74 or a pin 78 projectingfrom the device 9 so as to be maintained at a definite position (FIG. 28However, the hook 72 is moved in the reverse direction of arrow D,against the force of the spring 77, when the lever 75 is operated by apin 79 projecting from the upper portion of the cylinder 7, as well asby an inclined plane 72a provided at the front portion of the hook 72when the plane engages the pin 78.

operationally, in the embodiment shown in FIGS. 24 through 28, the firsthook 64 engages pin 68 so that the buckle-preventing device 9 isrestrained at the upper end portion of the cylinder when the piston-rodis in its contracted state (FIG. 25). When the inner boom member 3 hasbeen extended to an intermediate position, the first hook 64 leaves thepin 68 with the aid of the roller 66 and the cam 70, and the second hook72 becomes automatically engaged with the pin 78 due to the engagementof the inclined plane 72a and pin. Thereafter, the device 9 is movedtogether with the piston-rod 5 during extension thereof, so that saidprovided on the inner circumference of the inner boom device 9 ispositioned at an intermediate position of the inner boom member 3 (FIG.24). When the piston-rod 5 is contracted from the above state, thedevice 9 is moved together with'the contraction of the piston-rod 5 andthe pin 68 is passed along the inclined plane 64a to engagethe firsthook 64. At the same time, the

second hook 72 is moved intothe reverse direction of arrow D, due to theoperation of the lever by the .pin 79, and is released fromengagementwith the pin 78 so that the piston-rod 5 is further contracted to itsoriginal state. Therefore, the device 9 can be maintained substantiallyin the middle of piston-rod 5 when the latter is in its fully extendedposition.

In each of embodiments of the present invention, as shown in FIGS. 17through 28, the buckle-preventing means can be constructed such that,when the pistonrod has been extended by a definite distance, thebuckle-preventing device is moved to a predetermined point on theextended piston-rod, said piston-rod being supported at a suitableintermediate position by the buckle-preventing device which is slidablyor rotatably engaged with the inner circumference of the outer or innerboom member, and the maximum span of the piston-rod between the deviceand the free end of the piston-rod and between the device and thecylinder always being kept shorter than said definite distance, forexample, about a half of the length of the fullyextended piston-rod,whereby resistance against buckling of the extended piston-rod isincreased correspondingly. thus, according to the present invention, theweight of such a hydraulic cylinder unit can be decreased in proportionto the increase in resistance against buckling of the piston-rod. Inaddition, when utilizing an inverted or upside-down hydraulic cylinderunit, the buckle-preventing device is kept in contact with the lower endof the cylinder until the cylinder unit has been extended to anintermediate state, as is the case in the embodiments shown in'FIGS. l7and 18 and FIGS. 21 through 23, namely when the device is moved only atthe beginning period of extending operation and the closing period ofcontracting operation of the hydraulic cylinder unit. Therefore, thebucklepreventing device is moved before the piston-rod has a chance tobuckle, so that the device can be moved in'a substantially smoothmanner. Furthermore, when an inverted or upside-down cylinder unit isemployed, the cylinder of such unit can be pivoted or fixed to the innerboom member at'the lower end portion of said member whereby to increasethe resistance against buckling.

In addition, although a two-stage extensible boom is illustrated in eachof the embodiments shown in FIGS.

17 through 28, each feature particularly disclosed in preventing devicein each of the embodiments, except for that embodiment shown in FIG. 20,each feature particularly disclosed in said embodiment can be ap- Iplied, so long as no contradiction results, to modifiedbuckle-preventing means wherein two or more than two buckle-preventingdevices are provided to a pistonrod, and each of said devices is broughtto a controlled position when the piston-rod is extended.

Thus, the present invention is in no way limited to the embodimentsparticularly described hereinbefore, and it is to be understood thatinnumerable variations, applications, modifications and extensions ofthe basic principles involved may be made without departing from itsscope. The invention is to be limited, therefore, only by the scope ofthe appended claims.

What is claimed is:

1. In an extensible boom of the type having at least one pair oftelescopically extensible inner and outer boom members and at least onehydraulic power unit arranged between the ends of adjacent inner andouter boom members for producing relative movement between said boommembers, said power unit including a hydraulic cylinder connected to oneof said boom members, and a piston rod connected to the other of saidboom members; buckle-preventing means for said piston rod, saidbuckle-preventing means comprising: a body portion slidably received onsaid piston-rod of said power unit, said body portion having outwardlyextending means movably engaged with the inner circumference of the boommember to which the end of the piston is connected, and driving meansfor moving said body portion through said boom in response to theextending and contracting operation of said hydraulic cylinder unit,said driving means including means operably connecting said body portionto said adjacent boom members moving said body portion continuouslyduring said extending and contracting operation as a function of therelative movement between said members and at a rate smaller than theextending and contracting rate of said hydraulic cylinder unit, wherebysaid body portion is substantially continuously maintained intermediatethe end of said piston-rod connected to the other boom member and theend of said cylinder. t

2. A device according to claim 1 wherein said driving means includes afirst pulley mounted to said body portion and rope means fixed at oneend to a suitable portion of a boom member carrying said cylinder, saidrope means being trained over and around said pulley and fixed at itsother end to one end of a boom member carrying said piston-rod, secondand third pulleys mounted to opposite ends of said piston-rod carryingboom member, a fourth pulley mounted to 'said body portion, and secondrope means fixed at one end to one end of said cylinder carrying boommember, said second rope means being trained over and around saidsecond, third and fourth pulleys in such a manner that said latter ropemeans is turned at each of said latter three pulleys in aU-letter-shaped manner, and is fixed at the other end to the other endof said piston-rod carrying boom member.

3. A device according to claim 1 wherein said driving means includesfirst rack means fixed within the boom member carrying said cylinder,second rack means fixed within the boom member carrying said piston-rodand in confronting relationship with said first rack means, and pinionmeans positioned between and in engagement with said rack means, saidpinion means being connected to said body portion for moving the latterin response to the extending and contracting operation of said cylinder.

4. A device according to claim 3 wherein said first and second rackmeans includes a plurality of first racks provided around and mounted tothe outer circumference of said cylinder, an equal plurality of secondracksprovided around and mounted to the inner circumference of saidinner boom, each of said second racks being in confronting relationshipwith a corresponding one of said first racks, and an equal plurality ofpinion means for supporting said cylinder, each of said-pinion meansbeing provided between and in engagement with a confronting pair of saidracks.

5. A device according to claim 4 wherein said rack means is fixed at oneend to its corresponding boom member and wherein said driving meansfurther includes roller means supporting said last mentioned rack meansfor ensuring engagement between said pinion means and said lastmentioned rack means.

6, A device according to claim 1 wherein said driving means includes aplurality of roller means connected to said body portion, said rollermeans being in rotatable engagement with relatively movable surfacescarried by said inner and outer boom members, respectfully, whereby tomove said body portion.

7. A device according to claim 6 including a first elongated platemember positioned within and affi'xed to one of said boom members, asecond elongated plate member positioned within and affixed to theadjacent boom member, said plate members providing said relativelymovable surfaces for rotatable engagement with said roller means.

8. A device according to claim 7 wherein one of said plate members isfixed at one end to its corresponding boom member and wherein saiddriving means further includes second roller means mounted to the otherboom member, said second roller means being positioned for rotatableengagement with said last mentioned plate member whereby to aid insupporting said last mentioned plate member.

9. A device according to claim 8 wherein one of said plate members isfixed at one end to its corresponding boom member and wherein saiddriving means further includes second roller means rotatably mounted toa bearing provided with said first roller means, said second rollermeans being in rotatable engagement with said last mentioned platemember for insuring engagement between said first roller means and saidlast mentioned plate member.

10. A device according to claim 9 wherein said roller -means includes afirst roller rotatably engaging both of said plate members, a secondroller rotatably engaging said first plate member and a third rollerrotatably engaging said second plate member.

11. A device according to claim 1 wherein said driving means includesdrum means rotatably mounted to said body portion, a pair of rope meanssecured at common ends to said drum means and at opposite common ends tosaid adjacent boom members respectively and means for rotatably biasingsaid drum in a direction such that said ropes are wound thereupon.

- UNITED STATES PATENT OFFICE, M CERTIFICATE OF CORRECTION I Patent No.3 722 154 v Dated M h 21 ]913 Inven tor(s) Ter ya gak g I :1 kg j 11;]sh: mura fi Osamu Takarada.

It is certified 'that error appears in the above-identified patent v andthat said Letters Patent are hereby corrected as shown below:

C01. 13, line 30, after"members" insert v---amd- Signed and sealed this20th day of November-1973.

(SEAL)- Attest:

EDWARD M.FLETCHER,JR. RENE D. TEGTMEYER Attestinq Officer ActingCommissioner of Patents FORM P C-I050 (10-69) USCOMM-DC 66376-P69 or us.coy snuuzm r'nirgnqc OFFICE: Ins o-ssrsu

1. In an extensible boom of the type having at least one pair oftelescopically extensible inner and outer boom members and at least onehydraulic power unit arranged between the ends of adjacent inner andouter boom members for producing relative movement between said boommembers, said power unit including a hydraulic cylinder connected to oneof said boom members, and a piston rod connected to the other of saidboom members; bucklepreventing means for said piston rod, saidbuckle-preventing means comprising: a body portion slidably received onsaid piston-rod of said power unit, said body portion having outwardlyextending means movably engaged with the inner circumference of the boommember to which the end of the piston is connected, and driving meansfor moving said body portion through said boom in response to theextending and contracting operation of said hydraulic cylinder unit,said driving means including means operably connecting said body portionto said adjacent boom members moving said body portion continuouslyduring said extending and contracting operation as a function of therelative movement between said members and at a rate smaller than theextending and contracting rate of said hydraulic cylinder unit, wherebysaid body portion is substantially continuously maintained intermediatethe end of said piston-rod connected to the other boom member and theend of said cylinder.
 2. A device according to claim 1 wherein saiddriving means includes a first pulley mounted to said body portion andrope means fixed at one end to a suitable portion of a boom membercarrying said cylinder, said rope means being trained over and aroundsaid pulley and fixed at its other end to one end of a boom membercarrying said piston-rod, second and third pulleys mounted to oppositeends of said piston-rod carrying boom member, a fourth pulley mounted tosaid body portion, and second rope means fixed at one end to one end ofsaid cylinder carrying boom member, said second rope means being trainedover and around said second, third and fourth pulleys in such a mannerthat said latter rope means is turned at each of said latter threepulleys in a U-letter-shaPed manner, and is fixed at the other end tothe other end of said piston-rod carrying boom member.
 3. A deviceaccording to claim 1 wherein said driving means includes first rackmeans fixed within the boom member carrying said cylinder, second rackmeans fixed within the boom member carrying said piston-rod and inconfronting relationship with said first rack means, and pinion meanspositioned between and in engagement with said rack means, said pinionmeans being connected to said body portion for moving the latter inresponse to the extending and contracting operation of said cylinder. 4.A device according to claim 3 wherein said first and second rack meansincludes a plurality of first racks provided around and mounted to theouter circumference of said cylinder, an equal plurality of second racksprovided around and mounted to the inner circumference of said innerboom, each of said second racks being in confronting relationship with acorresponding one of said first racks, and an equal plurality of pinionmeans for supporting said cylinder, each of said pinion means beingprovided between and in engagement with a confronting pair of saidracks.
 5. A device according to claim 4 wherein said rack means is fixedat one end to its corresponding boom member and wherein said drivingmeans further includes roller means supporting said last mentioned rackmeans for ensuring engagement between said pinion means and said lastmentioned rack means.
 6. A device according to claim 1 wherein saiddriving means includes a plurality of roller means connected to saidbody portion, said roller means being in rotatable engagement withrelatively movable surfaces carried by said inner and outer boommembers, respectfully, whereby to move said body portion.
 7. A deviceaccording to claim 6 including a first elongated plate member positionedwithin and affixed to one of said boom members, a second elongated platemember positioned within and affixed to the adjacent boom member, saidplate members providing said relatively movable surfaces for rotatableengagement with said roller means.
 8. A device according to claim 7wherein one of said plate members is fixed at one end to itscorresponding boom member and wherein said driving means furtherincludes second roller means mounted to the other boom member, saidsecond roller means being positioned for rotatable engagement with saidlast mentioned plate member whereby to aid in supporting said lastmentioned plate member.
 9. A device according to claim 8 wherein one ofsaid plate members is fixed at one end to its corresponding boom memberand wherein said driving means further includes second roller meansrotatably mounted to a bearing provided with said first roller means,said second roller means being in rotatable engagement with said lastmentioned plate member for insuring engagement between said first rollermeans and said last mentioned plate member.
 10. A device according toclaim 9 wherein said roller means includes a first roller rotatablyengaging both of said plate members, a second roller rotatably engagingsaid first plate member and a third roller rotatably engaging saidsecond plate member.
 11. A device according to claim 1 wherein saiddriving means includes drum means rotatably mounted to said bodyportion, a pair of rope means secured at common ends to said drum meansand at opposite common ends to said adjacent boom members respectivelyand means for rotatably biasing said drum in a direction such that saidropes are wound thereupon.